Automatic test equipment for checking printed circuit boards has long involved use of a large number of spring-biased test probes arranged in a test fixture to make electrical contact under spring pressure with designated test points on the circuit board under test. Any particular circuit laid out on a printed circuit board is likely to be different from other circuits, and when the circuit to be tested is designed, a pattern of test points to be used in checking it is selected, and a corresponding array of test probes is configured in the test fixture. This typically involves drilling a pattern of holes in a probe plate to match the customized array of test probes and then mounting the test probes in the drilled holes on the probe plate. The circuit board is then mounted in the test fixture during testing, superimposed on the array of test probes. During testing, the spring loaded test probes are brought into spring pressure contact with the test points in the circuit board under test. Electrical test signals are then transferred from the board to the test probes and then to the exterior of the fixture for communication with a high speed computer operated electronic test analyzer which detects continuity or lack of continuity between various test points in the circuits on the board. At the end of each test, the test unit produces a pass/fail signal to indicate that the board has either passed or failed the test.
It has been common in the prior art for the operator to visually monitor a display or other means for indicating the results of the pass/fail test. The operator then manually separates the good boards from the bad boards. The good boards may be identified by manually stamping an identifying mark on the board. This approach leads to human error; experience has shown that some boards that have been tested will end up in the wrong group of boards.
Thus, it is desirable to provide a system for separating good boards from bad boards that leaves no room for human error. The procedure for identifying the good boards and bad boards should be accomplished not only with complete reliability, but also with minimal delay time in the testing process. In addition, any procedure for identifying the good boards should be done in such a way that an identifying mark on the board is permanent so it can distinguish the good boards from those that failed the test with 100% reliability.